Last summer, I mounted the Rolf Prima Ralos CXC 29er carbon-rimmed wheels to my Niner in preparation for the Trans-Sylvania Epic stage race. I wanted something lightweight to ease the climbing, and at 1527g for the pair (with thru-axle and XX1 XD Driver configuration), they met that criteria. They’re also wide, measuring in at 20.54mm internally. Full specs, measurements and pics are in our Unboxed intro.

The big unknown was whether the minimalist paired spoke design and carbon rims would hold up to the rocks and long, rapid descents of Pennsylvania’s mountains. And then the rest of the year’s worth of riding. And be stiff enough under a roughly 200lb rider load (me + clothes + pack + water).

The terrain certainly put them to the test. Not only were their plenty of rocks and high speed hits, but I managed to poke enough holes in a tire on one day that sealant simply couldn’t cope. Right in the middle of an enduro section on the enduro stage, after the second flat I’d had enough and decided to push on for the remainder of the timed segment. Pedaling and riding over roots, rocks and trail with nothing but a flaccid piece of rubber between rim and ground, I could hear things crunching, banging and grinding. Stupid? Perhaps, but wait until you see the damage…

The race started on Schwalbe’s Rocket Ron Snakeskin, which are light and fast, but their XC tires force you to choose between sidewall or tread protection. A lightweight tire with both simply isn’t offered by the German brand yet. Sure enough, all 13 of the punctures were in the tread bed, sidewalls were perfect. There were simply too many big cuts for the sealant to work. We tried a CO2 and it was like a garden sprinkler pinwheel of sealant. So, the second half of the weeklong race was ridden out on Maxxis Ikons.

The wheels come pre-taped with Stan’s NoTubes yellow tape. Both brands of tires seated up easily and held a nicely rounded profile. To me, that suggests the ~28mm outer/20.5mm inner width is a sweetspot for 2.2ish tires. The bead hook is thick and the rims finish with a smooth, curved shape that didn’t damage the tire’s sidewalls despite riding almost two miles with a flat rear tire. It even held onto the tire while flat.

They also held air really well (which, I know, has as much to do with the tires as the wheels) despite running them without the recommended rubber strip on top of the tape. Given that it’s sold as an option, I’d have a hard time recommending it since the performance was so good without it. And it adds 73g per wheel. I did take one corner particularly hard with really low pressure and the tire squirmed enough to let some grass get jammed between the bead and rim, which forced a stop to flick it out and pump it back up. I removed the crud with my finger, then reinflated with a mini-pump and it re-seated the tire quickly and easily.

So, looking for that damage? So was I. After riding a fair portion of two separate enduro segments on a flat rear tire, I expected complete carnage. What I found was a few small scrapes. Flesh wounds, really, and minor ones at that. These pics sum up the entirety of damage.

A few superficial scrapes barely made it through the clear coat, and the semigloss finish has muted a bit.

This little section of scratches on the rim edge were literally the only “significant” bits of damage I could find.

Following the TSEpic, these wheels saw another 6+ months of normal XC and trail riding with zero issues. From a handling perspective, I threw them into corners both sharp and wide and they tracked perfectly. The extremely light weight meant they spooled up quickly for sprints, too. What’s more, they were still visually true after all that. That’s one of the great benefits of carbon rims – they’re so stiff that a lightweight wheel performs extremely well under aggressive riding and they maintain their trueness long after an alloy rim would be warped silly. I had to perform zero maintenance on them during the test period. In fact, the only time I had to think about them was to consider just how freakin’ fast they let me be.

Honestly, there’s nothing I didn’t like about the Ralos CXC. I loved them. I didn’t want to give them back. I even liked the aesthetics of the paired spokes. I would (and regularly do) recommend these for anyone looking for a bombproof XC wheelset.

Rolf Prima makes various Ralos models, but the CXC is the only carbon one, and it’s only for 29ers. For those running standard cassettes, it comes with a machined titanium freehub. The XX1 freehub (tested) is steel also titanium, and parts are user interchangeable. Front wheel is available with a Lefty hub, too. At $1,799 they’re on low side of carbon XC wheels on the market.

There’s nothing like an overly wide rim to expose sidewalls to damage. Wider isn’t always better- especially when riding off road. You know, with rocks and stuff.

That said, the extra 0.46mm of inside will definitely make the Stan’s ride better. The internets said so.

Psi Squared - 01/13/14 - 3:48pm

@Tim A: That extra 0.46mm of internal width will translate to roughly a 7% increase in volume. That’s not insignificant, especially when you consider that you can also drop the air pressure.

Yes, simple geometry is hard…….for some.

Tim A - 01/13/14 - 4:20pm

@PSI,

Geometry is hard. Luckily, I just completed my GMAT, so it’s fresher for me than it had been for 20 years. Let’s walk through this:

A 2.2in tire measures 55.9mm across, which (simplifying to a round cross section) provides a circumference of 175.6mm. Without getting overly complex (I know that the rim represents a chord rather than arc length), increasing that by .46mm gets you a circumference of 176mm. Working that larger diameter, the width of the tire goes to 56.0mm.

Because (for a given wheel size) cross sectional area can be used in place of volume (both areas are multiplied by the same number), we’ll use that: The smaller rim gets an area of 2,452mm^2, the larger rim gets an area of 2,463mm^2.

If I’ve done my math right (feel free to check), the difference in volumes would be 0.43%- and likely imperceptible on the trail.

JasonK - 01/13/14 - 4:29pm

Game, set and match to Tim A!

Tim A - 01/13/14 - 4:31pm

@Tyler,

Sorry for taking this waaay off topic. The wheels look cool and the fact that they’re delivering this wheelset (with US-made White Industries hubs, I think) for under $2k is impressive.

@PSI,

I just checked my math- the volume difference would be .52%, the width/height difference 2.6%.

All – Some of the other top brands I checked are 18-20mm wide internal, and some, like Nox, are wider. Something to consider with wider rims: Some make mounting narrower 2.0 and 2.1 tires harder. In fact, I couldn’t get the WTB Nine Line tires to mount on the Nox XC 29er rims at all despite a LOT of effort, time, sealant and compressors. More on that in a review down the road. I’ve had the same issue with Ellsworth’s alloy wheels…they’re just too wide for some tires.

Tim A – thanks for the math!

Loki - 01/13/14 - 5:21pm

this is the ugliest bike i have ever seen… and the saddle looks like it has been adjusted by a supermarket sales person. but nothing to complain about these wheels!

Steve Scarich - 01/13/14 - 5:41pm

I have been using paired-spoke Shimano road wheels for over 10 years, 20K miles and still perfectly true, so paired-spoke can work.

This might sound crazy, but there is a real danger in paired spoke wheels. I know of at least three friends who have had accidents with paired-spoke wheels, when something (branch, squirrel) got lodged in their front wheel. Might not happen with 32 spokes, because you don’t have big gaps. One friend was actually killed, when a squirrel jumped into his front wheel, he endoed, broke his neck….true story. However, he was riding on the road through a park.

Chsad - 01/13/14 - 6:26pm

What size ikon and ron are on the bike pictured?

Psi Squared - 01/13/14 - 8:45pm

Tim A: I mistakenly had an extra r factor, so my first calculation should have been roughly 4%.

When I calculate the tire width (length from bead to bead) for a 2″ tire on a rim with an 18mm internal width, I got a length of 157.2mm. Then when I use that to calculate a new tire internal radius on a rim with an 20.54mm internal width and then further calculate the cross sectional area of the tire on both rims, I get 2501.7 mm^2 vs. 2434.5 mm^2. For the x-section area of the rims, I used a bead hook height of 6mm, so those x-section areas are 123.2mm^2 vs. 108mm^2. Add it all up and the total areas are 2624.9mm^2 vs. 2542.5mm^2, a difference of 3.2%. Given that you can run lower pressure with the larger tire volume, I suspect a rider could very well sense the ride quality difference since the volume difference isn’t that small.

Tim A - 01/13/14 - 10:24pm

PSI,

It looks like you’re using a different pair of rims (18mm & 20.54mm) and a narrower tire than I am. If I plug in those numbers and add a simple 6mm x [width] rim section, then I get numbers very close to yours. The discussion was comparing 21.54 and 22mm rims- and I used the 2.2in tire mentioned in the text- with the rim section added the difference is still down around 0.6%. I think that if you ran those components you’d see something similar.

In any case, I was taking the mick out of anyone who claimed that they could feel a sub-mm difference in rim widths while riding- and getting a bit of a mental workout at the same time. Besides, “That extra 0.46mm of internal width will translate to roughly a 7% increase in volume” just didn’t seem right (something on which we agree).

But the question should be “what’s so special about volume?” Sure, we can estimate it, but I would argue that the distance from the crown of a tire to the edge of the bead (a “cushion depth”), combined with the geometry of the tire’s sidewall (acting as a secondary spring) would be what allows riders to run lower pressures. Arguably, there’s nothing magical about volume per se. But that’ a discussion for another time and someone smarter than me. In the meantime, thanks for the mental exercise.

Hobbanero - 01/14/14 - 12:08am

Geek fight!

A useful bit of work as I contemplate the NOX rims or even the Wide Lightnings. Tim A’s question in the last para is a good one? What would 1mm of bead width theoretically mean in terms of being able to drop psi and have the same rim protection?

Jakey - 01/14/14 - 8:32pm

Given the same tire, a wider rim changes the contact patch slightly so that it is wider, and shorter front-to-back. Therefore the angle that the tire flexes at the front and back of the contact patch is less. The flexing of the tread rubber is the largest component of rolling resistance in a bicycle tire, so naturally less flex = less hysterisis losses = less rolling resistance. A tire with a larger volume of air will also serve to absorb bumps from rocks, roots, and uneven ground. So instead of wasted up-and-down motion, the bicycle wheel travels in a more linear, forward direction. There is, of course, a diminishing return for going with wider tires for any given trail. At some point you’re just adding weight (cough.. derby …cough).

Sir Ebral Cortez - 01/15/14 - 3:27pm

If i lower the pressure 10 lbs, will they be 10 lbs lighter?

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